輸入端之運動即為動力螺桿，其可轉換旋轉運動為直線運動於輸出端。利用小螺腹角可放大旋轉矩為下壓力。

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Input motion by the screw, it's circular motion can be transmitted into linear motion upon the output end. With a screw of small lead angle, torque can be amplified into pressure.